1. Field of the Invention
The present invention relates to a method of in-situ bio-remediation or chemical remediation of contaminated soil and groundwater, and more particularly to a method of supplying ultrasonic or vibratory energy to the contaminated soil to aid in the migration of the treatment solution through the soil.
2. Description of the Related Art
It is well known to perform in-situ remediation of contaminated soils utilizing oil eating bacteria. Large cost savings can be realized by remediating soil without having to dig the soil up. For example, U.S. Pat. No. 5,120,160 discloses injecting contamination consuming bacteria and water into the soil to be treated.
One problem with in-situ remediation by conventional methods is that is that it is difficult to ensure that the oil-eating consuming bacteria will reach all of the areas of the contamination because of the varying permeability of the soils encountered. At one extreme is sand, which easily conducts the treatment solution and evenly distributes it. Thus, the solution can easily reach several feet away from the perforated pipe. At the other extreme is clay, which is substantially impermeable, allowing virtually no movement of the solution therethrough. In such a case, bacteria laden water inserted into the ground will not be able to disperse through the clay soil to attack the oil. Most soils, in fact, are a blend between clay and sand, making effective dispersion difficult.
Methods to improve the dispersion of the bacteria include mechanically mixing the soil, as disclosed in U.S. Pat. No. 5,275,513. However, mechanically mixing the soil is expensive, bordering on the old "dig it up" methodology.
Another method to remediate contaminated soil is to extract the contaminants from the soil by electroosmosis. In this method, as disclosed in U.S. Pat. No. 5,240,570, an electric field is applied to the region of the soil being treated and the treatment solution is moved through the soil. However, this technique is complex and requires the presence of groundwater to deliver the bacteria.
U.S. Pat. No. 5,098,538 combines D.C. electrical energy and low frequency acoustic energy to aid in bacteria migration. Although this method is an improvement over electroosmosis, it is expensive and depends on a plurality of different parameters.
None of the prior art methods involve the use of ultrasonic or vibratory energy to aid in bacteria or chemical migration through contaminated soil. Although the use of ultrasonics is known to cavitate soil to prevent the germination of seeds (see, e.g., U.S. Pat. No. 3,902,273), ultrasonic energy has not been previously used for the purpose of increasing the permeability of soil.
Vibratory rollers are commonly used at construction sites to achieve higher soil densities and compaction. The units usually operate at approximately 1750 cycles per second, which appears to be the minimal natural frequency of soil. However, vibratory rollers have not been previously used in combination with fluid delivery for bio-remediation.